1. Field of the Invention
The present invention relates to a structure for stretching a pin of a chain and attaching a pin tip to an end of the pin, the chain being for engaging and conveying a container with a bottom, such as a can or bottle.
2. Related Art
Recently, aluminum or steel cans have been often used for containers of drinks such as beer or juice. A large number of the cans are manufactured and bottled with drinks in factories. When the cans are manufactured, many steps such as a step of printing on an outer circumferential face, a step of drying, and a step of coating the inside are necessary. In each of the steps, the cans are conveyed by a pin chain conveyor. FIG. 9 shows aluminum cans 102 being conveyed while being engaged by pin tips 101 of a pin chain conveyor 100. Of course, steel cans are conveyed in the same way.
Speed of the aluminum cans 102 being conveyed while being engaged by the pin tips 101 of the pin chain conveyor 100 is extremely fast, about 200 m/min. Therefore, since the aluminum cans 102 engaged by the pin tips 101 are moving without rest, scratches are induced on the insides of the cans by rubbing of the cans with the pin tips 101. The scratches cause imperfect coating of the inside of the aluminum cans. As a result, corrosion is induced by bottled drinks, resulting in reduction in quality of the drinks bottled in the aluminum cans 102.
The “pin chain conveyor” disclosed in JP-A-7-149417 is configured to be able to prevent deformation of an open edge of a can. That is, a pin chain conveyor has a chain to be conveyed, pins projecting from the chain, pin tips to be attached to ends of the pins, the pin tips being reversely covered with cylinders having bottoms and having cylindrical outsides; wherein the pin tips are longer than the height of the cylinders having bottoms, and end portions at a chain side of the pin tips are formed in a taper shape having a tapered end. However, while the open edges of the cylinders engaged by such pin tips are not deformed while being conveyed, scratches cannot be prevented from being induced on the inside.
FIGS. 10A to 10C show a conventional attachment structure of a pin tip attached to a pin. A pin tip 104 shown in FIG. 10A has a small outer diameter size, and is directly pressed to fit with a pin 103. In some cases, a retention process is performed to prevent separation of the pin tip 104 from the pin 103.
A pin tip 105 shown in FIG. 10B has a reverse truncated cone shape, and is set on a coil spring 107 which is set on and supported by a ring plate 106 attached to the pin 103. A fixing tool 108 is attached to a front end of a pin such that the pin tip 105 is not separated from the pin 103. Accordingly, the pin tip 105 can be lowered while compressing the coil spring 107 when load is exerted from above, so that the aluminum can 102 being conveyed can be supported and conveyed without receiving an impact.
An attachment structure of a pin tip 109 shown in FIG. 10c is similar to that of FIG. 10B, except that the coil spring 107 and the ring plate 106, which support the pin tip 109, are configured to be accommodated in a recess formed at a lower end portion of the pin tip 109. Therefore, the structure has an appearance that the coil spring 107 and the ring plate 106 are not exposed outside of the pin tip 9.
If the pin tips 105 and 109 are supported by the coil spring 107 as shown in FIGS. 10B and 10C, when load is exerted, the coil spring 107 is compressed and deformed so that the pin tips 105 and 109 can slide and move downward along the pin 103, which prevents scratches from being induced on the inside of the aluminum can 102 being conveyed. However, such an attachment structure cannot be used for the pin tip 104 having a small size as shown in FIG. 10A. Therefore, there has been a difficulty that the large pin tip 105 or 109 as shown in FIG. 10B or 10C cannot be used for conveying a bottle or can having a small port, and consequently impact force is exerted between the pin tip and the aluminum can 102 being conveyed, causing scratches on the inside of the can.